Wireline formation tester can easily lead to jamming of apparatus owing to the demand of apparatus structure and operation. The formation tester possesses a pushing and setting device and the device comprises a probe and a support arm. During borehole operation, the probe and support arm of the pushing and setting device are extended and contact the wall of a well, forming setting.
For measuring pressure and sampling at a fixed point location under a well, the time for logging often lasts for several hours, sometimes even tens of hours. Particularly, when the specific gravity of mud is larger and consequently the difference between formation pressure and mud column pressure in the wellhole reaches over 10 MPa, long-time operation at a fixed point location can easily lead to adhesion and jamming of the formation tester under the well. After the formation tester is jammed, the measurement must be interrupted to refloat apparatus, thus increasing the measurement cost and impacting the normal proceeding of measurement.
Enhanced Formation Dynamic Tester (EFDT) adopts the design of double probes and double support arms, reliable pushing mechanism ensures that the apparatus can release wireline for well logging during long-time operation under the well, avoiding mud adhering to the wireline and jamming, greatly reducing the chance of jamming of formation tester. But in the well where the pressure difference between formation pressure and mud column pressure in the wellhole is too large and mud cake is thick, EFDT apparatus will also suffer differential pressure sticking, by this time, even if releasing wireline for well logging, apparatus jamming cannot be avoided. Therefore, the technology of preventing jamming by releasing wireline used by EFDT at present cannot solve the problem of apparatus adhesion and jamming.